simple-luhn 0.1.0

Simple luhn implementation
Documentation 
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pub fn luhn(num: &str) -> bool {
    let mut sum = 0;
    let mut double = false;

    for ch in num.chars().rev() {
        if let Some(mut digit) = ch.to_digit(10) {
            if double {
                digit *= 2;
                if digit > 9 {
                    digit -= 9;
                }
            }
            sum += digit;
            double = !double;
        } else {
            // Non-digit character -> invalid
            return false;
        }
    }
    sum % 10 == 0
}